Abstract: A method for producing a steel material for line pipes which has a tensile strength of 570 MPa or more, a compressive strength of 440 MPa or more, and a thickness of 30 mm or more, the method including heating a steel having a specific composition to a temperature of 1000° C. to 1200° C.; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature +20° C.) or less is 50% or more, and a rolling finish temperature is the Ar3 transformation point or more and 790° C. or less; and subsequently performing accelerated cooling from a cooling start temperature of the Ar3 transformation point or more, at a cooling rate of 10° C./s or more, until the temperature of a surface of a steel plate reaches 300° C. to 500° C.

Abstract: A method for producing a steel material for line pipes which has a tensile strength of 570 MPa or more, a compressive strength of 440 MPa or more, and a thickness of 30 mm or more, the method including heating a steel having a specific composition to a temperature of 1000° C. to 1200° C.; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature +20° C.) or less is 50% or more, and a rolling finish temperature is the Ar3 transformation point or more and 790° C. or less; and subsequently performing accelerated cooling from a cooling start temperature of the Ar3 transformation point or more, at a cooling rate of 10° C./s or more, until the temperature of a surface of a steel plate reaches 300° C. to 500° C.

Abstract: A method for producing a steel material for line pipes including heating a steel having a specific composition to a temperature of 1000° C. to 1200° C.; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature +20° C.) or less is 50% or more, and a rolling finish temperature is the Ar3 transformation point or more and 790° C. or less; subsequently performing accelerated cooling from a temperature of the Ar3 transformation point or more, at a cooling rate of 10° C./s or more, to a cooling stop temperature of 200° C. to 450° C.; and then performing reheating such that the temperature of a surface of the steel plate is 350° C. to 550° C. and the temperature of the center of the steel plate is less than 550° C.

Abstract: Provided is a steel pipe for a linepipe having high compressive strength, a heavy wall thickness and sour gas resistance. The steel pipe has the composition which contains by mass % 0.02 to 0.06% C, 0.01 to 0.5% Si, 0.8 to 1.6% Mn, 0.012% or less P, 0.0015% or less S, 0.01 to 0.08% Al, 0.005 to 0.050% Nb, 0.005 to 0.025% Ti, 0.0005 to 0.0035% Ca, 0.0020 to 0.0060% N, and Fe and unavoidable impurities as a balance. The steel pipe has metal microstructure where a fraction of bainite is 80% or more, a fraction of M-A constituent is 2% or less and an average grain size of bainite is 5 ?m or less.

Abstract: Provided are a steel pipe for a linepipe with high compressive strength and a heavy wall thickness, and a method of manufacturing the same. Lowering of yield stress caused by a Bauschinger effect can be suppressed by optimizing the metal microstructure of a steel plate without requiring particular forming conditions in forming the steel pipe, and without requiring heat treatment after pipe making. A steel pipe has the composition which contains by mass % 0.03 to 0.10% C, 0.30% or less Si, 1.00 to 2.00% Mn, 0.015% or less P, 0.003% or less S, 0.080% or less Al, 0.005 to 0.035% Nb, 0.005 to 0.020% Ti, and Fe and unavoidable impurities as a balance. The steel pipe has metal microstructure where a fraction of bainite is 60% or more, a fraction of rolled ferrite is 5% or less, and a fraction of M-A constituent (MA) is 3% or less.

Abstract: A line pipe having a wall thickness of 20 mm or more and a tensile strength of 560 MPa or more and a production method therefor are provided. The base metal portion contains particular amounts of C, Si, Mn, P, S, Al, Nb, Ca, N, and O, one or more component selected from Cu, Ni, Cr, Mo, V, and Ti as optional components, and the balance being Fe and unavoidable impurities. The microstructure in the pipe thickness direction contains 90% or more bainite and 1% or less of MA in a region that extends from a position 2 mm from an inner surface to a position 2 mm from an outer surface. In a hardness distribution in the pipe thickness direction, the hardness in a region other than a center segregation area is 220 Hv10 or less and the hardness in the center segregation area is 250 Hv10 or less.

Abstract: A line pipe and a production method therefor are provided. The microstructure in the pipe thickness direction contains 90% or more bainite in a region that extends from a position 2 mm from an inner surface to a position 2 mm from an outer surface. In a hardness distribution in the pipe thickness direction, the hardness in a region other than a center segregation area is 220 Hv10 or less and the hardness in the center segregation area is 250 Hv0.05 or less. The major axes of pores, inclusions, and inclusion clusters that are present in a portion that extends from a position 1 mm from the inner surface to a 3/16 position of the tube thickness and in a portion that extends from a position 1 mm from the outer surface to a 13/16 position of the tube thickness in the tube thickness direction are 1.5 mm or less. A continuous casting slab having the above-described composition is hot-rolled under particular conditions and then subjected to accelerated cooling.

Abstract: In an abrasion resistant welded steel pipe, each of a base material and a weld metal contains specific amounts of chemical composition. The base material of the abrasion resistant welded steel pipe has a Vickers hardness within the range of 150 to 250, and the weld metal has a Vickers hardness within the range of 230 to 350. A weld heat affected zone in the abrasion resistant welded steel pipe has a Vickers hardness within the range of 150 to 350. In the weld metal, the dispersion density of a sulfide having an aspect ratio of 5 or more and containing at least one selected from Fe, Mn, and Ti is 10 grains/mm2 or less. The abrasion resistant welded steel pipe that can be produced at high productivity and low cost with no reduction in weld crack resistance can be provided.

Abstract: A welded steel pipe with excellent welded heat-affected zone toughness includes a butt weld formed by prior welding either an inner surface or an outer surface with a single layer for each of the inner and outer surfaces, wherein in the metallographic structure of a welded heat-affected zone, the martensite-austenite constituent (MA) area fraction is 4% or less, the average prior-austenite grain size is 400 ?m or less, and the following items are taken into account: the average prior-austenite grain size of a welded heat-affected zone formed by prior welding, the average prior-austenite grain size of a welded heat-affected zone formed by subsequent welding, the bead width determined at a position 5 mm apart from the tip of a weld bead formed by subsequent welding, the fusion line tilt angle of a weld bead of prior welding, and the fusion line tilt angle of a weld bead of subsequent welding.

Abstract: Provided is a steel pipe for a linepipe having high compressive strength, a heavy wall thickness and sour gas resistance. The steel pipe has the composition which contains by mass % 0.02 to 0.06% C, 0.01 to 0.5% Si, 0.8 to 1.6% Mn, 0.012% or less P, 0.0015% or less S, 0.01 to 0.08% Al, 0.005 to 0.050% Nb, 0.005 to 0.025% Ti, 0.0005 to 0.0035% Ca, 0.0020 to 0.0060% N, and Fe and unavoidable impurities as a balance. The steel pipe has metal microstructure where a fraction of bainite is 80% or more, a fraction of M-A constituent is 2% or less and an average grain size of bainite is 5 ?m or less.

Abstract: Provided are a steel pipe for a linepipe having a heavy wall thickness and excellent fracture toughness in a base material, and methods of producing the same. A welded heat affected zone is achieved by suppressing lowering of yield stress caused by a Bauschinger effect by optimizing the metal microstructure of a steel plate. A steel pipe has a composition which contains by mass % 0.03 to 0.08% C, 0.10% or less Si, 1.00 to 2.00% Mn, 0.010% or less P, 0.0030% or less S, 0.06% or less Al, 0.005 to 0.020% Nb, 0.005 to 0.025% Ti, 0.0010 to 0.0060% N, and Fe and unavoidable impurities as a balance. Ti(%)/N(%) is a value which falls within a range of 2 to 4, and a Ceq value is 0.30 or more.

Abstract: Provided are a steel pipe for a linepipe with high compressive strength and a heavy wall thickness, and a method of manufacturing the same. Lowering of yield stress caused by a Bauschinger effect can be suppressed by optimizing the metal microstructure of a steel plate without requiring particular forming conditions in forming the steel pipe, and without requiring heat treatment after pipe making. A steel pipe has the composition which contains by mass % 0.03 to 0.10% C, 0.30% or less Si, 1.00 to 2.00% Mn, 0.015% or less P, 0.003% or less S, 0.080% or less Al, 0.005 to 0.035% Nb, 0.005 to 0.020% Ti, and Fe and unavoidable impurities as a balance. The steel pipe has metal microstructure where a fraction of bainite is 60% or more, a fraction of rolled ferrite is 5% or less, and a fraction of M-A constituent (MA) is 3% or less.